This invention relates to the manufacture of a solid electrolytic capacitor, and more particularly to the use of a manganese nitrate impregnating solution containing a surfactant to reduce ridging of the manganese dioxide formed during subsequent pyrolysis.
The prior art has described the problems in obtaining even coatings of manganese dioxide on anodized valve-metal pellet anodes. One problem has been the degradation of the anodic oxide during repeated pyrolyses. In order to reduce the number of repetitions of the impregnation-pyrolysis sequence, thickeners or other means of increasing the viscosity of the manganese nitrate solutions have been employed. Another problem has been that ridges of manganese dioxide develop along the edges of the pellets during the pyrolytic conversion of manganese nitrate to the dioxide. Formation of these ridges cause two problems: thicker than desirable manganese dioxide coatings along the edges of the pellets, and thinner coatings elsewhere on the pellet surfaces. The problem is particularly acute when the pellets are rectangular.